Characteristics of Asphaltene Fractions Responsible for the Formation of Stable Water‑Oil Emulsions

Stable water-oil emulsions are formed due to the strong armor layer at the oil/water interface able to prevent the coalescence of water droplets in oil. The stability of water-oil emulsions obtained by mixing solutions of asphaltene in toluene and in heptol (a mixture of n-heptanol and toluene) with distilled water was found to be a function of two asphaltene fractions, namely, a fraction soluble in heptol enriched with ester fragments and a fraction tending to form aggregates in heptol. The surfactant properties of the first fraction permit the formation of a thin shell with low mechanical strength at the oil/water interface. The asphaltene aggregates adsorbed onto this thin shell are compacted over time, imparting rigidity and mechanical strength to the oil/water interface layer.